Spectrochemical analysis

ABSTRACT

1. Excitation apparatus useful in spectrochemical analysis comprising means for holding a sample to be spectrochemically analyzed, MEANS FOR DIRECTING A COHERENT BEAM OF PHOTONS ONTO SAID SAMPLE WITH SUFFICIENT ENERGY TO DISLODGE A PORTION TO BE ANALYZED FROM THE SAMPLE, AND AUXILIARY MEANS FOR RAISING THE EXCITATION ENERGY OF THE DISLODGED PORTION SO PRODUCED TO CAUSE EMISSION, WITHIN A SPECTROSCOPICALLY EXAMINABLE FIELD, OF ELECTROMAGNETIC RADIATIONS CHARACTERISTIC OF CHEMICAL ELEMENTS PRESENT IN SAID DISLODGED PORTION.

United States Patent Schuch et al.

[451 Aug. 1,1972

SPECTROCHEMICAL ANALYSIS Inventors: John A. Schuch, Weston; Frederick Brech, Dover, both of Mass.

Assignee: Fisher Scientific Company, Pittsburgh, Pa.

Filed: Feb. 25, 1963 Appl. No.: 260,412

U.S. Cl ..356/86 rm. Cl. ..G01j 3/30 Field of Search ..331/94.5; 88/14 SE; 356/86 [56] References Cited OTHER PUBLICATIONS Runge et al., Micro-Analysis of Metals by Optical Emission Spectroscopy, Applied Spectroscopy; Vol. 13, No.3, 1959; pg. 74- 76. QC45lAlA6 Black, Lasers Cast Light on Machining, Welding Problems, Tool & Manufacturing Engineenvol. 48,

No. 6, June 1962, pp; 85- 91. (Pages 90 & 91 relied upon). TJl 180.AlT64 Primary Examiner-Ronald L. Wibert Assistant Examiner-V. P. McGraw Attorney-Willis M. Ertman EXEMPLARY CLAIM l. Excitation apparatus useful in spectrochemical analysis comprising means for holding a sample to be spectrochemically analyzed,

means for directing a coherent beam of photons onto said sample with sufficient energy to dislodge a portion to be analyzed from the sample, and auxiliary means for raising the excitation energy of the dislodged portion so produced to cause emission, within a spectroscopically examinable field, of electromagnetic radiations characteristic of chemical elements present in said dislodged portion.

15 Claims, 2 Drawing Figures SPECTROCHEMICAL ANALYSIS This invention relates to spectrochemical analysis and more particularly to anovel means and mode for producing, in a spectroscopically examinable field, electromagnetic radiation characteristic of all the chemical elements contained in a sample to be analyzed for resolution into an orderly spectrum by conventional spectroscopic examination.

Spectrochemical analysis is a well-known technique in which samples are analyzed by placing them between two poles in an electrical circuit, across which poles an electrical discharge is made to occur, thereby causing the samples to emit electromagnetic radiations. When a sample, however, contains two components, in close juxtaposition, one of which is electrically conductive and another of which is not electrically conductive, excitation of the non-conductive component does not often occur.

It is also well-known in emission spectroscopy that samples to be analyzed may not be uniform in their composition, and detailed information of segregation or discrepancies or departures from uniformity frequently is desired. Attempts to achieve this in optical emission spectroscopy have involved the use of needlepointed counter electrodes in apposition to the sample such that the position at which spark energy is received is located at a predetermined area. However, only very limited success has been achieved with this system.

More recently, microemission analyses have been conducted with anexcitation system known as the electron or x-ray microprobe. In such instrumentation, the sample is usually placed within an evacuated chamber and in such a position that a fine stream of high speed electrons may be directed at a predetermined point on the sample. The absorption of electron energy results in the emission of x-radiation from the sample, which xradiation is characteristic of all the elements that the sample spot irradiated comprises. The emission of such radiation may be analyzed into component frequencies by an x-ray diffractometer or an x-ray spectrometer and from the definition of the presence of specific frequencies reduced to elemental metal stratums.

The electron microprobe provides certain limitations to the scope of the analysis. Most important of these is that radiation from those elements in the periodic table, including titanium element No. 22, downwards to beryllium element No. 4 and lithium element No. 3, is of so long a wave length as to be wholly absorbed in an air or other gaseous path. Techniques for the analysis of such radiations require burdensome vacuum apparatus and even then the long wave lengths are difficult to sort out, requiring the use of organic crystals which often are unstable under radiation.

The primary object of this invention is to provide novel and improved excitation means for spectrochemical analysis, which operates independently of the electrical conductivity of the components of the sample, is comprehensive to all elements of the periodic table, and is reliably useful in the analysis of microsized as well as macrosized samples.

Another object of the invention is to provide novel and improved spectrochemical analysis apparatus employing a coherent beam of photons as a sample energizing source.

A further object of the invention is to provide novel and improved spectrochemical analysis apparatus utilizing two coordinated energizing sources for raising all the chemical elements in a precise portion of the sample material under investigation to spectroemissive energy levels.

This is accomplished in accordance with this invention by utilizing a coherent beam of photons to cause vaporization of a portion of the test sample. Energy sufficient for these purposes is available in a coherent light beam derived, for example, from an optical maser available'on the market (Trion Instruments Co., Ann Arbor, Mich); and may be sufficient, depending upon the nature of the sample, to cause excitation to spectroemissive energy levels of some or even all of the atoms of the test sample. (For most elements such energy levels are in the order of l to 15 electron volts.) However, the efficiency of excitation produced in this manner is a function of the thermoconductivity of the sample. When, for example, the sample is a poor thermal conductor, such as a refractory, ionized vapor may be readily produced by the coherent beam of photons which has detectable radiation characteristic of all the elements present in the vapor. Many materials, however, are not sufiiciently excited, with the energies and pulse durations available from present day optical masers, to emit reliably detectable radiations characteristic of all the elements in the sample.

Accordingly, auxiliary means is provided for raising the vapor components to spectroemissive energy levels in order to assure emission of detectable electromagnetic radiations characteristic of all the elements in the vaporized sample. Stimulation of the vapor is caused preferably by electrical means with the presence of the vapor being obtained through impingement of a coherent light beam on the sample.

A preferred apparatus for spectrochemical analysis in accordance with this invention is illustrated in the accompanying drawing, .in which:

FIG. 1' is a diagram in perspective form of the apparatus; and

FIG. 2 is a schematic diagram of the optical arrangement and the electrical circuitry employed in the apparatus.

A sample S to be tested is placed on a suitable stage 12 for receiving a pulse from optical maser 14, through pulse time control means 16, a prism 18 and a focusing element 20. The maser 14 may be a ruby rod that is energized by a flash lamp and power is supplied to the maser by a conventional power supply 22. The maser, for example, may have an output power of 0.1 to 1.0 joules and a pulse width in the order of 40 to microseconds which is narrower than the normal pulse width in the order of l millisecond of optical masers described in the literature. A narrow pulse width has been found to be particularly useful in analyzing samples of highelectrical conductivity.

An auxiliary lens system including an optical eye piece 24, a pivoted mirror 26 and the focusing element 20 which may be a microscope objective provides a view on the surface of the sample S which may be in the order of 40 to 100 microns in diameter. This auxiliary lens system may be employed for positioning the sample so that the area of interest is precisely located relative to the spot of impingement of the maser beam. The

mirror 26 is pivoted out of the path of the coherent beam of photons from the maser 14 when the sample is to be excited. The focusing element 20 acts to concentrate the photon beam to dimensions as small as 5 microns for use in analyzing ceramic material for example..

Between the sample S and the microscope objective 20 are a pair of cross electrodes 28,30 across which a voltage of some 1,000 to 3,000 volts may be impressed at the time that .the maser pulse occurs. As indicated in FIG. 2, these electrodes may be energized from an electrical source 32 across which a microfarad capacitor 34 is connected. The electrodes 28,30 are in the series discharge circuit of the capacitor which includes a 100 microhenry inductance 36 and a total circuit resistance in the order of 1 ohm (represented by 38).

A suitable radiation detector such as a spectrograph involving the usual slit 40, prism 42, and focal curve 44 is oriented to examine the resulting electromagnetic radiations in the optical range emitted by the vapor excited by the electrode discharge.

In operation, the sample 8 is positioned through the use of the auxiliary lens system and then the mirror 26 is moved out of the path of the photon beam. The maser 14 is operated and the resulting coherent beam of photons strikes the selected sample area, raising all the material in the selected area to at least dissociative energy levels in a vaporizing action. A relatively narrow maser pulse width may be employed when energizing thermally conductive samples so as to vaporize only a small, precisely selected area, whereas pulses of longer duration may be utilized with lessconductive materials or to analyze larger areas. As the photon beam may not raise all the elements in the energized area of the sample to spectroemissive energy levels, an auxiliary energizing means including the electrodes 28,30 is employed. This auxiliary means insures that all the elements are raised to their spectroemissive energy levels for detection by the spectrograph. As the vapor emitted from the sample rises in a conical column into the area between the electrodes, the electrostatic field there created is distorted so that an arc breakdown across the electrodes results which discharges capacitor 34. This energy discharge is of a magnitude sufficient to' raise all the elements in the sample to spectroemissive energy levels so that they generate detectable characteristic radiations which are sensed by the spectrograph. The auxiliary energy imparted to the vaporized sample may occur as the result of the discharge of the capacitor just prior to or simultaneously with the maser pulse, the gap between the electrodes being such that a discharge occurs thereacross only when vapor emanating in a column from the sample S enters the gap.

While the analysis may take place with atmospheric ambient conditions, the sample .may, if desired, be placed in a controlled atmosphere so as to prevent reaction of the sample with the components of ambient air. While the drawing illustrates the use of spaced electrodes as the auxiliary energizing means, other auxiliary sources of energy may be utilized, for example radio frequency energy generated as by a Tesla coil, a spark or arc between electrodes having a voltage drop of the order of 60 volts or'a second coherent photon beam from a second maser whose pulse is focused on the vaporized column in timed relation .to the first maser pulse. In some instances, as previously stated, the

maser pulse may be of sufficient energy to excite all the atoms I in the vaporized column to spectroemissive levels and, in other instances, a double pulse from 5 maser 14 may be so arranged that the first pulse vaporizes and the second pulse further excites the vapors. These energizing means secure sufficient excitation of the vapor as will insure reliable readings with minimum destruction of the sample and are almost, if not entirely, independent of its thermal conductivity and atomic number. As can be realized, microsize contaminants and inclusions can be readily examined without resort to electron microprobe techniques and without physical contact with the sample.

While a preferred embodiment of the invention has been shown and described, various modifications thereof will occur to those skilled in the art, and therefore it is not intended that the invention be limited to the disclosed embodiment or to details thereof and departures may be made therefrom within the spirit and scope of the invention as defined in the claims.

We claim:

1. Excitation apparatus useful in spectrochemical analysis comprising means for holding a sample to be spectrochemically analyzed,

means for directing a coherent beam of photons onto said sample with sufficient energy to dislodge a portion to be analyzed from the sample,

and auxiliary means for raising the excitation energy of the dislodged portion so produced to cause emission, within a spectroscopically examinable field, of electromagnetic radiations characteristic of chemical elements present in said dislodged portion.

2. Excitation apparatus useful in spectrochemical analysis comprising means for holding a sample to be spectrochemically analyzed,

means for directing a coherent light beam onto said sample with sufficient energy to dislodge a portion of the sample to be analyzed,

and auxiliary means for raising the excitation energy of, the dislodged portion so produced to cause emission, within a spectroscopically examinable field, of electromagnetic radiations characteristic of all the chemical elements present in said vapor. 3. Excitation apparatus useful in spectrochemical analysis comprising means for holding a sample to be 50 spectrochemically analyzed,

electrode means defining a gap adjacent said sample holder means, means to create an electric field across said gapfand means for directing a coherent beam of photons onto 55 said sample with sufficient energy to eject a portion to be analyzed from the sample into said gap to cause breakdown of said electric field and cause emission, within a spectroscopically examinable field, of electromagnetic radiations characteristic of chemical elements present in said ejected portion. 4. Apparatus useful in spectrochemical analysis comprising a maser having its axis oriented to direct a coherent beam of photons onto a surface area of a sample to be spectrochemically analyzed with sufficient energy to cause emanation from such sample of a column of vaporized material,

auxiliary means for raising the excitation energy of the vaporized material so produced to cause emission, within a spectroscopically examinable field, of electromagnetic radiations characteristic of all the chemical elements present in said vaporized material,

and means for spectroscopically examining said radiations.

5. Apparatus useful in spectrochemical analysis com prising an optical maser having its axis oriented to direct a coherent light beam onto a surface area of a sample to be spectrochemically analyzed with sufficient energy to cause emanation from such sample of a column of vaporized material,

a pair of spaced electrodes defining a gap therebetween which intersects the path of the vapor column so emanating from said sample,

means for impressing an electric potential across said electrodes to raise the excitation energy of vapor emanating into said gap and cause emission therefrom of electromagnetic radiations characteristic of all the chemical elements in said vapor,

and means for spectroscopically examining said radiations.

6. Spectrochemical analysis apparatus comprising a source of a coherent beam of photons,

means for holding a sample of material to be analyzed,

means for directing said beam of photons onto said sample with sufficient energy to raise chemical elements in the portion of the sample subjected to said beam of photons to at least dissociative energy levels,

auxiliary means for raising chemical elements from dissociative energy levels to spectroemissive energy levels,

and means for sensing a change in radiation dueto the raised energy levels of said chemical elements in a spectrochemical analysis operation.

7. The spectrochemical apparatus as claimed in claim 6 wherein said photon beam directing means includes means for focusing said beam,

and further including optical means including said focusing means for visually inspecting the particular portion of said sample on which said beam is to impinge.

8. The spectrochemical analysis apparatus as claimed in claim 6 wherein said auxiliary means includes a pair of spaced electrodes positioned between said source of photons and said sample holder,

and means for establishing an electrostatic field between said electrodes having an energy potential sufficient to raise all the chemical elements in a vapor introduced between said electrodes to spectroemissive energy levels,

said electrodes being positioned relative to said sample holder so that vapor emitted from the sample as a result of impingement of the coherent beam of photons on said sample disturbs the electric field sufficiently to cause an electrical breakdown between said electrodes and a resulting transfer of energy to said vapor.

9. Apparatus useful in spectrochemical analysis comprising a maser for generating a coherent beam of photons in a pulse of less than 100 microseconds duration,

means for holding a sample of material to be analyzed,

means for directing said beam of photons from said maser onto said sample with sufficient energy to raise all the chemical elements in a portion of the sample subjected to said beam of photons to at least dissociative energy levels to produce a column of vapor,

and electric discharge means for subjecting the chemical elements in said column of vapor to supplemental excitation to raise said chemical elements in said column to spectroemissive energy levels to cause emission, within a spectroscopically examinable field, of electromagnetic radiations characteristic of all the chemical elements present in said sample portion.

10. The spectrochemical analysis apparatus as claimed in claim 9 wherein said supplemental excitation means includes a pair of spaced electrodes positioned between said maser and said sample holder,

said electrodes being positioned on opposite sides of the path of said beam of photons,

electrical energy storage means connected in circuit with said electrodes,

and means for energizing said electrical energy storage means to establish an electric field between said electrodes having an energy potential sufficient to raise the chemical elements in a vapor introduced between said electrodes to spectroemissive energy levels,

said electrodes being positioned relative to said sample holder so that vapor emitted from the sample as a result of impingement of the coherent beam of photons on said sample disturbs the electric field sufficiently to cause an electrical breakdown between said electrodes and release of energy from said storage means.

11. The apparatus .as claimed in claim 10 wherein said photon beam directing means includes means for focusing said beam on said sample,

and further including optical means including said focusing means for visually inspecting the particular portion of said sample on which said beam is to impinge.

12. Apparatus useful in spectrochemical analysis comprising a maser for generating a coherent beam of photons, 7

means for holding a sample of material to be analyzed,

means for directing said beam of photons from said maser onto said sample with sufficient energy to eject a column of particles from a portion of the sample subjected to said beam of photons,

a pair of spaced electrodes positioned between said maser and said sample holder,

said electrodes being positioned on opposite sides of the path of said beam of photons,

means for establishing an electrostatic field between said electrodes having an energy potential sufi'icient to raise all the chemical elements in said column introduced between said electrodes to spectroemissive energy levels,

said electrodes being positioned relative to said sample holder so that the column ejected from the sample as a result of impingement of the coherent beam of photons on said sample disturbs the electric field sufiiciently to cause an electrical breakdown between said electrodes,

and means for spectroscopically examining radiations resulting from said spectroemissive energy levels.

13. A method of spectrochemical analysis comprising directing onto a surface of a'material to be analyzed a coherent beam of photons having sufficient energy to cause emanation of a column of sample material,

raising the energy level of the particles in said column to cause emission of electromagnetic radiations characteristic of all the chemical elements in said column,

and spectroscopically examining said radiations.

14. A method of I spectrochemical anlaysis of a minute sample of material comprising directing onto a surface of the material to be analyzed a coherent light pulse of less than 100 microseconds duration, said pulse having sufficient energy to cause emanation of a column of sample material,

electrically raising the energy level of the particles in said column to cause emission of electromagnetic radiations characteristic of all the chemical elements in said column,

and spectroscopically examining said radiations.

15. A method of detecting a constituent element in a minute body within a sample of material comprising the steps of directing a beam of coherent waves of electromagnetic energy on said minute body, thereby causing a quantity of said minute body to be removed; exciting said quantity of said minute body sufficient to stimulate emission therefrom of electromagnetic energy having detectable characteristics; and detecting said characteristics.

i I? l 

1. Excitation apparatus useful in spectrochemical analysis comprising means for holding a sample to be spectrochemically analyzed, means for directing a coherent beam of photons onto said sample with sufficient energy to dislodge a portion to be analyzed from the sample, and auxiliary means for raising the excitation energy of the dislodged portion so produced to cause emission, within a spectroscopically examinable field, of electromagnetic radiations characteristic of chemical elements present in said dislodged portion.
 2. Excitation apparatus useful in spectrochemical analysis comprising means for holding a sample to be spectrochemically analyzed, means for directing a coherent light beam onto said sample with sufficient energy to dislodge a portion of the sample to be analyzed, and auxiliary means for raising the excitation energy of the dislodged portion so produced to cause emission, within a spectroscopically examinable field, of electromagnetic radiations characteristic of all the chemical elements present in said vapor.
 3. Excitation apparatus useful in spectrochemical analysis comprising means for holding a sample to be spectrochemically analyzed, electrode means defining a gap adjacent said sample holder means, means to create an electric field across said gap, and means for directing a coherent beam of photons onto said sample with sufficient energy to eject a portion to be analyzed from the sample into said gap to cause breakdown of said electric field and cause emission, within a spectroscopically examinable field, of electromagnetic radiations characteristic of chemical elements present in said ejected portion.
 4. Apparatus useful in spectrochemical analysis comprising a maser having its axis oriented to direct a coherent beam of photons onto a surface area of a sample to be spectrochemically analyzed with sufficient energy to cause emanation from such sample of a column of vaporized material, auxiliary means for raising the excitation energy of the vaporized material so produced to cause emission, within a spectroscopically examinable field, of electromagnetic radiations characteristic of all the chemical elements present in said vaporized material, and means for spectroscopically examining said radiations.
 5. Apparatus useful in spectrochemical analysis comprising an optical maser having its axis oriented to direct a coherent light beam onto a surface area of a sample to be spectrochemically analyzed with sufficient energy to cause emanation from such sample of a column of vaporized material, a pair of spaced electrodes defining a gap therebetween which intersects the path of the vapor column so emanating from said sample, means for impressing an electric potential across said electrodes to raise the excitation energy of vapor emanating into said gap and cause emission therefrom of electromagnetic radiations characteristic of all the chemical elements in said vapor, and means for spectroscopically examining said radiations.
 6. Spectrochemical analysis apparatus comprising a source of a coherent beam of photons, means for holding a sample of material to be analyzed, means for directing said beam of photons onto said sample with sufficient energy to raise chemical elements in the portion of the sample subjected to said beam of photons to at least dissociative energy levels, auxiliary means for raising chemical elements from dissociative energy levels to spectroemissive energy levels, and means for sensing a change in radiation due to the raised energy levels of said chemical elements in a spectrochemical analysis operation.
 7. The spectrochemical apparatus as claimed in claim 6 wherein said photon beam directing means includes means for focusing said beam, and further including optical means including said focusing means for visually inspecting the particular portion of said sample on which said beam is to impinge.
 8. The spectrochemical analysis apparatus as claimed in claim 6 wherein said auxiliary means includes a pair of spaced electrodes positioned between said source of photons and said sample holder, and means for establishing an electrostatic field between said electrodes having an energy potential sufficient to raise all the chemical elements in a vapor introduced between said electrodes to spectroemissive energy levels, said electrodes being positioned relative to said sample holder so that vapor emitted from the sample as a result of impingement of the coherent beam of photons on said sample disturbs the electric field sufficiently to cause an electrical breakdown between said electrodes and a resulting transfer of energy to said vapor.
 9. Apparatus useful in spectrochemical analysis comprising a maser for generating a coherent beam of photons in a pulse of less than 100 microseconds duration, means for holding a sample of material to be analyzed, means for directing said beam of photons from said maser onto said sample with sufficient energy to raise all the chemical elements in a portion of the sample subjected to said beam of photons to at least dissociative energy levels to produce a column of vapor, and electric discharge means for subjecting the chemical elements in said column of vapor to supplemental excitation to raise said chemical elements in said column to spectroemissive energy levels to cause emission, within a spectroscopically examinable field, of electromagnetic radiations characteristic of all the chemical elements present in said sample portion.
 10. The spectrochemical analysis apparatus as claimed in claim 9 wherein said supplemental excitation means includes a pair of spaced electrodes positioned between said maser and said sample holder, said electrodes being positioned on opposite sides of the path of said beam of photons, electrical energy storage means connected in circuit with said electrodes, and means for energizing said electrical energy storage means to establish an electric field between said electrodes having an energy potential sufficient to raise the chemical elements in a vapor introduced between said electrodes to spectroemissive energy levels, said electrodes being positioned relative to said sample holder so that vapor emitted from the sample as a result of impingement of the coherent beam of photons on said sample disturbs the electric field sufficiently to cause an electrical breakdown between said electrodes and release of energy from said storage means.
 11. The apparatus as claimed in claim 10 wherein said photon beam directing means includes means for focusing said beam on said sample, and further including optical means including said focusing means for visually inspecting the particular portion of said sample on which said beam is to impinge.
 12. Apparatus useful in spectrochemical analysis comprising a maser for generating a coherent beam of photons, means for holding a sample of material to be analyzed, means for directing said beam of photons from said maser onto said sample with sufficient energy to eject a column of particles from a portion of the sample subjected to said beam of photons, a pair of spaced electrodes positioned between said maser and said sample holder, said electrodes being positioned on opposite sides of the path of said beam of photons, means for establishing an electrostatic field between said electrodes hAving an energy potential sufficient to raise all the chemical elements in said column introduced between said electrodes to spectroemissive energy levels, said electrodes being positioned relative to said sample holder so that the column ejected from the sample as a result of impingement of the coherent beam of photons on said sample disturbs the electric field sufficiently to cause an electrical breakdown between said electrodes, and means for spectroscopically examining radiations resulting from said spectroemissive energy levels.
 13. A method of spectrochemical analysis comprising directing onto a surface of a material to be analyzed a coherent beam of photons having sufficient energy to cause emanation of a column of sample material, raising the energy level of the particles in said column to cause emission of electromagnetic radiations characteristic of all the chemical elements in said column, and spectroscopically examining said radiations.
 14. A method of spectrochemical anlaysis of a minute sample of material comprising directing onto a surface of the material to be analyzed a coherent light pulse of less than 100 microseconds duration, said pulse having sufficient energy to cause emanation of a column of sample material, electrically raising the energy level of the particles in said column to cause emission of electromagnetic radiations characteristic of all the chemical elements in said column, and spectroscopically examining said radiations.
 15. A method of detecting a constituent element in a minute body within a sample of material comprising the steps of directing a beam of coherent waves of electromagnetic energy on said minute body, thereby causing a quantity of said minute body to be removed; exciting said quantity of said minute body sufficient to stimulate emission therefrom of electromagnetic energy having detectable characteristics; and detecting said characteristics. 